1) Adjust oven racks to upper-middle and lower-middle positions and preheat oven to 250º. Set wire rack in aluminum foil-lined rimmed baking sheet and spray rack with non-stick spray.
2) Pat wings dry with paper towels and transfer to a large bowl. Combine baking powder and salt, add to wings, and toss to evenly coat.
3) Arrange wings, skin side up, in single layer on prepared wire rack. Bake wings on lower-middle oven rack for 30 minutes. Then move pan to upper-middle rack, increase temperature to 425º, and roast until wings are golden brown and crispy, 40-50 minutes longer, rotating sheet halfway through baking.
4) While wings are baking, combine sauce ingredients in bowl and whisk until smooth. Set aside.
5) Remove sheet from oven and let stand for 5 minutes. Transfer wings to bowl, add sauce (you may not need all of it), and toss to coat. Arrange on a serving platter and garnish with chopped scallions or sesame seeds.